As the wood board which is made by laminating veneer sheets by adhesive, glued laminated wood such as laminated lumber, plywood having veneer sheets laminated together such that any two adjacent veneer sheets are arranged with the wood grain thereof oriented perpendicularly to each other, laminated veneer lumber (LVL) in which constituent veneer sheets are laminated together with the wood grain thereof extending parallel to each other, etc. have been known in the art.
General demand for the wood board or panel is changing from plywood to a wood board such as oriented strand board (OSB), which is also referred to as waferboard, wherein the constituent element thereof is not veneer, but smaller pieces of wood called strands which are arranged with the wood grain thereof discrete or interrupted. A reason for such increasing demand for OSB is its greater in-plane shear strength as compared with plywood.
FIG. 6(A) schematically shows plywood in which one of two adjacent veneer sheets thereof has its wood grain extending substantially parallel to one side of the plywood board and the other of the two adjacent veneer sheets has its wood grain extending substantially perpendicular to the above one side of the plywood board, while FIG. 6(B) shows plywood of another type in which two adjacent veneer sheets thereof have their wood grain extending diagonally in opposite directions at about 45° so that the wood grain of the two veneer sheets are oriented perpendicularly to each other (straight and dotted lines in the square frame represent the wood grain directions of the two adjacent veneer sheets, respectively). FIG. 6(C) shows particleboard (PB). Values provided below the square frames in FIG. 6 represent the shear strengths of the respective board materials.
It has been known in the art that plywood which is made by clipping veneer sheets and arranging such clipped veneer sheets with the grain thereof oriented diagonally at about 45° with respect to the ends or lateral sides of the plywood board, as shown in FIG. 6(B), has a shearing strength that is greater than that of particleboard. As shown in FIG. 5, it has been also known that the shear modulus becomes the greatest when the veneer sheets are arranged with the wood grain thereof oriented diagonally at about 45° with respect to shear plane. It has been known in the art, therefore, that veneer sheets may be cut and arranged as shown in FIG. 6(B) to overcome drawbacks of conventional plywood.
Since it is considered that particleboard (PB) shown in FIGS. 5 and 6 has substantially the same elements orientation as the aforementioned OSB, the strength of particleboard is substantially the same as that of OSB and the following description will be made based on such assumption.
However, no such plywood is seen in actual market that is strengthened as described above. A decisive reason for such disuse is that cutting the existing plywood boards for production of the above plywood board will waste substantially half of the material. Thus, even the possibility of the presence of plywood or veneer laminated board of the above-described structure has been very little considered. If the veneer laminated board which overcomes the drawbacks of conventional plywood by having its constituent veneer sheets arranged and laminated together with the grain thereof oriented diagonally at about 45° with respect to the ends or lateral sides of the resulting board is reasonably manufacturable, demand for such board having outstanding characteristics and performance will be created and the provision of such board will be desired by the market.
As shown in the Publication of Laid-open Japanese Patent Application, No. H9-248803, it has been known in the art that a plywood board may be reinforced by providing between any two adjacent veneer sheets of the plywood board an additional veneer sheet whose wood grain are oriented at about 45°, or an angle between 20° and 70°, with respect to the ends or lateral sides of the plywood board.
However, according to this method in which ordinary rotary-cut veneer sheets are clipped diagonally into lozenged or diamond-like shaped veneer sheets, each lozenged veneer sheet is further clipped into a smaller-sized rectangular veneer sheet by cutting off triangular end portions and such rectangular veneer sheet is laminated between any two veneer sheets in the plywood. However, this method of manufacturing plywood is disadvantageous in terms of labor cost and material cost.
According to the method of manufacturing diagonal laminated veneer lumber of the present invention, the constituent veneer sheets are laminated together with the wood grain thereof oriented diagonally with respect to the longitudinal ends or the lateral sides of the resulting board, as a result of which a wood board having a high strength can be produced. Specifically, the method of the present invention is advantageous in that conventional machines and equipment for peeling veneer sheet and clipping such veneer sheet and also the conventional manufacturing line can be used for mass production of the diagonal laminated veneer lumber of the present invention with a small cost and no waste of material.
Such technical and economical effects can bring about other effects as follows.
(1) Presently, no wood board having an in-plane shear strength corresponding to that of OSB is manufactured. The advent of the diagonal laminated veneer lumber of the present invention, whose strength is greater than OSB, can be a new promising product for the plywood industry.
(2) Further processing the diagonal laminated veneer lumber, various kinds of wood products with high performance such as horizontal members or beams and structural wall board can be provided.
(3) One of typical applications where OSB is used in large quantities in North America is the web for I-beam (also called as I-joist), which is due to high in-plane shear strength of OSB as compared with plywood. Since the diagonal laminated veneer lumber has an in-plane shear strength that is still greater than that of OSB, the diagonal laminated veneer lumber can be an effective OSB replacement capable of providing I-beam of a still higher performance.
(4) As described above, using the diagonal laminated veneer lumber of the present invention, horizontal structural member with high strength capability can be made. Thus, the use of such material makes it possible to design a long-spanned architecture with a higher degree of freedom, and the quantities of wall, beam and pillar members for use and hence the total cost for such architecture can be reduced.
(5) Cedar that is one of the typical species of wood in Japan has been suffering from sluggish demand. Cedar has a high strength for its lightweightness and such characteristics of cedar can be enhanced to the greatest extent by the present invention. Thus, cedar can be utilized as a new material and the invention can contribute to promoting the demand of cedar. Additionally, the present invention can be used to promote the effective utilization of wood available from thinning forest.